Differential side gear and the production method thereof

ABSTRACT

The invention relates to a differential side gear comprising internal splines ( 11 ) which are used to connect a drive shaft. The inventive differential side gear comprises circular gear teeth ( 3 ) and defines a rectilinear blind hole ( 4 ) which is used to house and connect an end portion of the drive shaft. Said differential side gear comprises a single forged piece. The aforementioned circular gear teeth ( 3 ) and the blind hole ( 4 ) are disposed in a coaxial manner and are centred on a rotation axis (X-X′) of the differential side gear.

[0001] The present invention relates to a differential side gear, as well as to a method for producing such a side gear.

[0002] Within the meaning which is understood here, the shell of a differential is the rigid structure in which are mounted the side and pinion gears of this differential. In operation, it receives the movement that the differential has for its function to distribute between drive shafts, and it rotates on itself.

[0003] In the majority of auto-motive vehicles, the power of the drive motor is transmitted to the driving wheels via in particular a gear box and a differential. It is known to mount the differential inside the gear box, designed accordingly, and to provide that the shell of this differential does not completely envelop the side and pinion gears, the expression “lantern wheel differential” being commonly employed to designate a type of differential. Consequently, like the gears of the gear box, the differential and its side and pinion gears dip in the oil that the casing of this gear box contains.

[0004] In order to avoid the gear box losing oil, each side gear may be mounted, by means of a tight bearing, in a wall of the casing. In that case, it is important that the side gears themselves also be tight. Now, an axial passage for the housing of a drive shaft opens out at the two ends of each of the side gears, in order that these gears be able to be traversed on either side by a pin intended to hollow out therein, by removal of matter, internal splines for connection of the drive shaft. Consequently, an added obturator is mounted at one end of the passage defined by each side gear, whose tightness is thus ensured.

[0005] However, when a side gear thus constituted is produced in large quantities, there are always a few copies whose tightness is deficient.

[0006] The invention, which intends to overcome this drawback, therefore has for its purpose to propose a side gear which is more reliable in terms of tightness than the one which has just been described.

[0007] To that end, the invention has for its object a differential side gear, characterized in that it is provided with internal splines for connection of a drive shaft, in that it comprises circular gear teeth, in that it is forged in one piece and in that it defines a rectilinear blind hole for housing and connecting an end portion of the drive shaft, the circular gear teeth and the blind hole being coaxial and centred on an axis of rotation of the side gear.

[0008] The invention also has for its object a method for producing a side gear as defined hereinabove, characterized in that it comprises a step in which the splines are formed by axially engaging in said blind hole an internal die, comprising as many radial teeth as there are splines to be made.

[0009] The invention will be more readily understood on reading the following description given by way of example and made with reference to the accompanying single Figure which is a view in axial section of a side gear according to the invention.

[0010] This side gear P is essentially symmetrical with respect to its axis of rotation X-X′. It comprises a tubular portion 1 which extends in a radial ring 2. The periphery of this radial ring 2 presents the form of conical gear teeth 3, arranged in a circle symmetrical with respect to the axis of rotation X-X′.

[0011] The tubular portion 1 partially defines a blind hole 4. The latter extends in the radial ring 2 before reaching a radial end wall 5 which defines its bottom 6. From its opening 7, the blind hole 4 successively comprises a cylindrical portion 8, then a connecting or truncated convergent portion 9, and finally a substantially cylindrical portion 10. Internal splines 11 for connection, regularly distributed around the axis of rotation X-X′, are formed in the side gear P and extend axially over the major part of the length of the portion 10, in which the splined end portion of a drive shaft (not shown) is intended to be housed, with reduced clearance, and to couple with the side gear P. The portion 10 and the circular gear teeth 3 are thus coaxial and centred on the axis of rotation X-X′.

[0012] The side gear P is a single forged piece. The splines 11 are likewise forged. More precisely, they are extruded, i.e. obtained with the aid of an internal die (not shown), driven axially in the portion 10, towards the bottom 6, then withdrawn in the other direction. This internal die, which comprises as many radial teeth as there are splines 11 to be made, therefore makes a return journey, which renders the extrusion of the splines 11 compatible with the presence of the radial wall 5 forming obturator. Such is not the case in the known use of a pin for hollowing out by machining the splines of the side gear of the prior art, described in the preamble.

[0013] Moreover, the extruded splines are more robust than those obtained by machining.

[0014] Among the advantages of the invention, it will be noted that the side gear P which has just been described is simpler than the side gear of the prior art, described in the preamble. In particular, it comprises only one part to be manufactured, managed and stored, while the side gear of the prior art presents at least one more, namely the added obturator.

[0015] In addition, the tightness of the obturation of the passage in the side gear of the prior art is obtained only by a very precise machining of that portion of this passage in which the added obturator is mounted. Moreover, this part has a particular shape, intended to retain the obturator. The invention eliminates all these constraints, as well as another one, namely the necessity of effecting a check of the tightness of each side gear produced. 

1. Differential side gear, characterized in that it is provided with internal splines (11) for connection of a drive shaft, in that it comprises circular gear teeth (3), in that it is forged in one piece and in that it defines a rectilinear blind hole (4) for housing and connecting an end portion of the drive shaft, the circular gear teeth (3) and the blind hole (4) being coaxial and centred on an axis of rotation (X-X′) of the side gear.
 2. Side gear according to claim 1, characterized in that the splines (11) are extruded.
 3. Side gear according to claim 1, characterized in that a radial end wall (5), in one piece with said side gear, defines the bottom (6) of the blind hole (4).
 4. Side gear according to claim 1, characterized in that it comprises a radial ring (2) and a tubular portion (1), which defines at least a part of said blind hole (4), the ring (2) bearing the gear teeth (3) and extending the tubular portion (1).
 5. Side gear according to claim 1, characterized in that the opening (7) of the blind hole (4) and the circular gear teeth (3) are each localized at one of the two axially opposite ends of the side gear.
 6. Method for producing a side gear according to claim 1, characterized in that it comprises a step in which the splines (11) are formed by axially engaging in said blind hole (4) an internal die, comprising as many radial teeth as there are splines (11) to be made. 